Risk assessing dredging activities
Led by: Dr Ross Jones, AIMS
The project will use novel analytical techniques/instrumentation to accurately quantify, for the first time, key proximal stressors associated with dredging/spoil disposal (i.e. sedimentation, light quantity/quality, suspended sediment concentrations) and will determine how these parameters vary with increasing distance from dredging. We will then test the response of corals, sponges, seagrass and algae to environmentally relevant/realistic conditions over appropriate time-frames. Matrices of hard data will be generated to derive water quality thresholds for key habitat forming organisms and for use as input parameters for pressure field modelling (including cumulative-impact modelling). This will dramatically improve risk assessment processes, provide greater surety for regulators and proponents, allow more informed decision-making and inform future dredging policy.
Quantifying the spatial and temporal movement of pressure fields associated with maintenance dredging (and dredge material placement) and understanding (1) how this relates to natural background rates and (2) the physiology and ecology of sensitive key habitat-forming local biota in the short and long term, is essential for managing dredging projects using zonation schemes and for making sound, reliable predictions of the potential extent and severity of any effects.
The lack of accurate, published, empirical data on the in situ conditions associated with dredging is a key challenge for regulatory agencies and ports and without it, it is difficult to contextualize results from experimental studies of sediments on sensitive receptors (which have shown that re-suspended sediments are a hazard but not whether they pose a risk at different distances from dredging) and design environmentally realistic exposure studies to determine dose-response relationships.
Other immediate problems are that sedimentation, one of the key stressors, has never been accurately measured at the dredge site (due to lack of available technology) and we have recently been identified changes in light spectra underneath plumes, which has significant implications for WQ monitoring programs and impact prediction-based on light measurements.
Overall the influence of plume duration on foundation species has also not been adequately addressed, nor has the comparative sensitivity of adult life forms and early life stages that may lead to recruitment failure and changes at the population/community level.
How Research Addresses Problem
We are proposing a very pragmatic, practical, ecotoxicological approach to address these
challenges using a combination of:
- Desktop studies (examining water quality collected during past dredging projects and nondredging baseline conditions).
- Empirical field studies using newly developed sediment deposition sensors and techniques.
- Laboratory (aquarium) studies examining the effects of different proximal stressors on the physiology of key habitat-forming species such as corals, sponges, seagrasses and algae and including juvenile forms of some species to examine recruitment and population-level effects.
This information will be used to derive dose-response relationships for relevant cause-effect pathways using environmentally relevant exposure conditions. This fit-for-purpose research program will produce the critical information required to inform the generic management frameworks for designing and implementing water quality monitoring programs, for reactive management and for cumulative impact assessment purposes. We will use a risk-based approach to analyzing and interpreting the data and this combination of activities will support spatial mapping of potential effects of maintenance dredging activities, including zonation schemes and deliver definitive statements regarding long term chronic effects of sediments from dredging on local populations.
Alignment with NESP Research Priorities
Priority 4: Reducing Potential Impacts: Dredging activity
(4a) Determine critical turbidity and sedimentation tolerance thresholds for environmental resources likely to be influenced by dredging activities.
(4b) Quantify sediment transport pathways and water quality over relevant timeframes to better understand interactions with, and contributions to, the broader catchment inputs within the GBR.
Our proposal will also address elements of:
(4c) Understand the potential environmental risks associated with dredging activities, especially land-based disposal and reclamation, and identify impact mitigation techniques that will reduce identified significant risks.
Sedimentation; Water quality; Dredging; Risk assessment; Spatial effects.
This project is jointly funded through Port of Townsville Ltd, AIMS, JCU and the Australian Government’s National Environmental Science Programme.
Dr Muhammad Abdul Wahab is a sponge ecologist at AIMS, investigating the effects of suspended sediments from dredging on the early life history of the sponge Carteriospongia foliasens. He discusses some of the experiments being conducted in the AIMS National Sea Simulator (SeaSim) as part of Project 2.1.9 ‘Risk Assessing Dredging projects’ which is funded by the National Environmental Science Program (NESP) Topical Water Quality Hub. The project involves a number of studies including examining the effects of suspended sediments on swimming speeds of sponge larvae, the effects of light reduction (from suspended sediments) on sponge orientation in the water column, and effect of sediments on sponge settlement (See Dr Abdul Wahab talking about the project in the video below at 2 mins 44 seconds).
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